1. Field of the Invention
The invention generally relates to railway track maintenance equipment, and in particular to the manner of distribution of replacement railroad crossties or sleepers along a railway line during refurbishing of the track. A tie ejection apparatus is provided with a conveyor for queuing new ties and an endless drive chain mounted to a frame by a rotatable sprockets. Two striker plates are attached to the drive chain at opposite sides of the mounting frame. New ties are loaded from a storage car and transported by the conveyor to the tie ejection apparatus. The drive chain is rotated, for example under operator control, to bring one of the striker plates into endwise contact with each tie in turn, and to push the tie in one direction or the other from the distribution car to the side of the track. The placement of the tie along the track is repeatably determined by operation of the tie ejection apparatus in conjunction with an adjustable shield attached to the mounting frame, which deflects the tie at a pre-selected angle as it is pushed from the distribution car.
2. Prior Art
Railways comprise a bed of ballast material such as size four stones, in which ties are partly embedded to support rails attached to the ties at a specific gauge width, elevation and the like. The rails rest on tie plates and the rails and tie plates are fastened to the ties by spikes, bolts, clips or similar fasteners. In the United States, most rail ties are made of wood, which helps to absorb shock as trains pass. Concrete ties can also be used. Over time and with traffic, compressive and shearing forces damage the ties and loosen the fasteners. Ties also deteriorate due to weather. As a result, it is necessary to replace the ties as a matter of regular track maintenance.
Typically, ties are selected for replacement and preliminarily marked. The selected ties are disengaged from the rails by removing their fasteners, for example by pulling their spikes, and are pulled laterally from under the rails. A new tie is inserted. Tie plates, spikes and anchors are installed to couple the rail to the tie. The ballast is then rearranged by tamping and vibratory stabilization, often accompanied by realignment and elevational adjustments to the track. A selection of ties can be replaced, or all the ties can be replaced, in which case the tracks are lifted and rethreaded onto the new ties.
Railway ties are usually replaced using a number of special purpose rail cars that service a section of track while traveling over that section. Specialized rail cars may have one or more of spike pullers, tie extractors and inserters, tampers, stabilizers, etc., for serving the successive steps, including transporting new ties to the site and removing the old ties that have been extracted. It is efficient to use the same tie storage cars to bring new ties and to take away worn ties, namely by moving collected old ties to a location in the tie storage car from which new ties were previously unloaded, in a continuous operation. To accomplish this, in addition to having cars with storage space for ties, a track maintenance apparatus can include various transport conveyors, tie removal devices and cranes for manipulating the ties.
An example of a rail based tie exchange system is disclosed in commonly owned PCT Application No. PCT/US97/23156. A tie transfer rail vehicle exchanges old ties for new ties and comprises a plurality of gondola type cars with closed sidewalls and open tops. The tie exchanging operation commences with ties being drawn out from beneath the rails and placed on the rails for pick up by a tie pick-up device which can place the ties on a conveyor leading to an accumulating location. The tie pick-up car alternatively can have a collection cage at the front at track level, to pick up extracted ties left on the rails. A conveyor transports the ties to a temporary collection area from which they can be loaded into a storage car.
The storage cars hold both new ties for distribution and collected old ties, at least some of the space for storage of old ties being made available as the new ties are unloaded and distributed. A number of storage cars can be provided, for example coupled between a tie distribution car at the rear and a tie collection car at the front, in the direction of travel. Tie transport vehicles shuttle back and forth between a point where new ties are being unloaded and where they are distributed, and between a point at which old ties are being stored and where they are collected, respectively. The loading and unloading points vary as work progresses, for example both proceeding in one direction or the other between the front and rear of the apparatus. For allowing the tie transport vehicles (e.g., cranes) to pass between cars, the vehicles have flanged wheels and the storage cars have rails along their tops, including telescoping hinged sections which bridge between cars. One or more transport vehicles moves the old ties from the temporary tie collection area to the storage cars and loads and moves new ties from the storage cars to the tie distribution car where they are distributed alongside the rails for installation by a following apparatus.
Although this rail based tie exchange system accomplishes tie removal and distribution in an integrated manner, it distributes new ties using a ramped conveyor, which together with the periodic arrival of the transfer vehicle may discharge the ties intermittently. Assuming that sufficient ties are queued for discharge, they are discharged regularly, which may be useful for replacing all the ties on a track but is not useful for replacing irregular selected ties. Without good control of the position at which ties are discharged, before the ties can be placed under the rails it is often necessary to pick them up and move them. This extra step slows the replacement process. It would be helpful if each tie could be placed at the position where the tie is to be inserted. It would be even more helpful to precisely position and also orient the ties in a precise and repeatable manner.
An alternative to using a conveyor to distribute ties is disclosed in U.S. Pat. No. 5,467,717 -Theurer where a crane is used to pick up and place each tie individually. This permits the ties to be placed where they are to be installed and minimizes the need for an additional positioning step, but is very slow. A more efficient tie ejecting device is needed, which nevertheless allows controllable tie positioning and discharge at the point of installation.